THERMAL-KINEMATIC LINKAGES IN OROGENS
Orogenic processes operate at all scales, from the lithosphere to grain-scale, and are inexorably linked. Over the last two decades, numerical and theoretical models of collisional systems have become increasingly complex, allowing explicit coupling of fundamental processes such as kinematics, mechanics, and thermal evolution at the orogen scale. At the same time, significant advancements have been made in the comparative analysis of large multi-disciplinary, field derived datasets from a variety of orogens worldwide. To some degree, however, the progress achieved by this work is limited by our ability to reconcile what we observe in the field with model predictions. In the UK Structure and Geodynamics Group, we are coupling comprehensive field studies in a number of orogens with advanced computational modeling to test fundamental ideas in collisional tectonism.
At the scale of an orogenic wedge, mechanical and thermal strain continuum models indicate that bulk thermal architecture is governed by the inherent kinematic asymmetry of the pro- and retro-sides of the wedge. In natural systems, these zones are arguably more complex, as major orogenic components such as the high-grade hinterland, low-grade hinterland, and exterior foreland fold-thrust belt are generally separated by discrete faults and/or shear zones. These boundaries commonly accommodate substantial thrust and in some cases normal sense displacement of 10's to 100's kms. Displacement of this magnitude can lead to juxtaposition of rocks that do not share a common protolith and, perhaps most importantly, finite deformational and thermal history. Observation of the latter indicates that these structures exert a critical influence on the thermal evolution (and by association controls deformational style through temperature-dependent rheology) of collisional systems and highlights our need to understand this thermal-kinematic linkage. Our group uses the Scottish Caledonides as a natural laboratory to investigate how crustal-scale thrust faults influence the thermal architecture of orogenic systems and how that thermal architecture controls the rheological response of the wedge. To do this, we integrate detailed field work, quantitative pressure-temperature and geochronologic analyses, and finite-element modeling.
This study is being conducted in conjunction with collaborators Kyle Ashley (University of Texas, Austin), Richard Law (Virginia Tech), Geoff Lloyd (University of Leeds, UK), Rob Strachan (University of Portsmouth, UK), and Calvin Mako (Virginia Tech).
coupling between upper and lower crusTal processes in an exhumed orogenic channel
The channel flow hypothesis represents one of the most novel and perhaps controversial orogen-scale geodynamic models ever proposed to explain how large collisional systems accommodate shortening. As is common with paradigm shifting ideas such as this one, the presence of channel flow tectonics was conceptually, and often qualitatively, proposed to explain observations in a number of other collisional orogens worldwide. In the UK Structure and Geodynamics Group we are coupling field investigations in the Nepal-India Himalayas and southern Appalachians with advanced numerical modeling to test linkages between upper and lower crustal processes in regions of presumed crustal flow.